This invention relates to optical switches and in particular to an optical switch having a plurality of switching positions.
In optical communication systems it is often necessary to switch an optical signal between different optical paths, be it along an optical waveguide such as an optical fiber, or in free space. Optical switching devices may generally be classified into moving-beam switches and moving-fiber switches. Moving-beam switches redirect the optical signal path between stationary waveguides or in free space. Moving-fiber switches physically change the location of optical fibers to be switched.
Different categories of optical switches for switching optical signals include electrical switches, solid-state switches, mechanical switches, and optical switches and combinations therebetween.
Electrical switches convert an optical signal to an electrical signal and then switch the electrical signal by conventional switching techniques. Electrical switches then convert the electrical signal back into an optical signal. Electrical switches are faster then existing mechanical switches but are also significantly more expensive. Furthermore, electrical switching of optical signals is bandwidth limited since a converted electrical signal can not carry all the information in an optical signal. This bandwidth limitation of electrical switches severely limits the advantages of using fiber optics.
Solid-state optical switches have fast switching speeds and the same bandwidth capacity as fiber optics. However, the cost for solid-state optical switches is 30 to 100 times more than those for existing mechanical switches. Another disadvantage of solid-state optical switches is that they incur insertion losses exceeding 20 times those for existing mechanical optical switches.
Mechanical optical switches are typically lower in cost than electrical or solid-state optical switches, provide low insertion loss, and are compatible with the bandwidth of fiber optics
The activation mechanism used in the optical deflection switch of the present invention is a moving-beam switch mechanism.
An exemplary optical fiber switch that utilizes a moving mirror to perform the switching function is disclosed by Levinson in U.S. Pat. No. 4,580,873 issued Apr. 8, 1986 which is incorporated herein by reference. Although this invention appears to adequately perform its intended function, it is believed too costly and somewhat complex.
There have been several designs of optical deflection switches using Frustrated Total Internal Reflection (FTIR) to accomplish switching or modulation of an optical signal. In almost all cases these systems begin with air gap which produces total internal reflection, and then rapidly drives the material to less than one tenth wavelength spacing to produce frustrated total internal reflection. Such systems are disclosed in U.S. Pat. Nos. 4,249,814; 3,649,105; 3,559,101; 3,376,092; 3,338,656; 2,997,922; and 2,565,514. In all of these systems there is a problem in overcoming friction and damage to the glass.
Another exemplary moving-beam optical switch that redirects the optical signal path between stationary waveguides is disclosed in U.S. Pat. No. 5,444,801 to Laughlin incorporated herein by reference. The invention described therein teaches an apparatus for switching an optical signal from an input optical fiber to one of a plurality of output optical fibers. This apparatus includes means for changing the angle of the collimated beam with respect to the reference so that the output optical signal is focused on one of the plurality of output optical fibers. Similar mechanical optical switches are disclosed in U.S. Pat. Nos. 5,647,033; 5,875,271; 5,959,756; 5,555,558; 5,841,916; and 5,566,260 to Laughlin incorporated herein by reference.
Laughlin teaches switching of optical signals between input fibers and output fibers through shifting of one or more virtual axis of the system by changing the position of a second reflector between multiple positions. This second reflector has a wedge shape to change the angle of the collimated beam by a selected amount to direct the beam to different output locations. However, the output locations are all lying along a diameter in the output focal plane of the GRIN lens as shown in FIG. 1.
It is an object of the invention to provide an optical deflection switch having more switching positions than provided for in Laughlin""s prior art optical switches. This is achieved by using the output focal plane of a lens more effectively.
Further, it is an object of the invention to provide an optical deflection switch in which the output beam is more confined to the center of the lens as in comparison to prior art optical switches while still being able to switch an optical signal to a plurality of fibers.
In accordance with the invention there is provided an optical deflection switch comprising: a) a tapered block of a light-transmissive material having a reflective surface and a second face, the second face including an input/output port and the reflective surface for providing reflection of a beam of light passing through the input/output port in to the tapered block; b) a first block of a light-transmissive material having a first face and a second face, the first face including an input port thereon for receiving a collimated beam of light and the second face for providing total internal reflection of the beam of light in a first switching state and for acting as an output/input port for optical communication with the input/output port of the switching block when the total internal reflection is frustrated in a second switching state, and an angle defined between the reflective face of the switching block and the second face of the second block being other than zero; and c) a rotator for turning the switching block around an axis into one of a plurality of selectable positions, each of the plurality of selectable positions for changing a plane of incidence of the beam of light.
In accordance with the invention there is further provided an optical deflection switch comprising: a first block of a light-transmissive material having an input port and a plurality of output ports at an end face thereof; and a switching block of a light-transmissive material having at least two non-parallel outer faces, said switching block being optically coupled with the first block in at least a first switching mode, and wherein the switching block is relatively rotatable with the first block in the at least first switching mode for reflecting a beam of light to the output ports, said beam of light being received from the input port.